This invention relates particularly to sewing machines, especially those incorporating automatic work guidance, but it will be understood that the invention could as well apply to other types of machines employing other tools, not necessarily needles.
When multi-needle sewing machines are employed on work relatively movable in a plane perpendicular to vertically reciprocable needles (or other tools) a component of work feeding movement along a line parallel to the line interconnecting the needle tips alters the spacing of each seam from the general sewing path and changes the spacing of one seam from an adjacent seam. This may produce unattractive results from the standpoints of appearance and structurally due to unequal stitch lengths. In order that the predetermined direction of movement of the workpiece at any moment be tangent with the stitch path, as often required for instance in lockstitch seams, zig-zag stitching, and chain stitch seams, it is necessary that the work, or the machine, or a portion of the latter, be relatively rotated about an operating axis. The present invention is in some embodiments directed to providing automatic relative rotation of the needle bar and hook or other stitch-forming assembly to maintain this desired tangency relation. In a broader aspect, the invention contemplates controlled rotation of a tool-carrying member about an axis normal to a plane in which the work is being predeterminedly advanced with X and/or Y components for processing, to maintain and/or predeterminedly change angular relation of the operating localities of a tool or tools carried by the member with respect to the path of movement of the work.
In U.S. Pat. No. 3,139,051, there is disclosed an arrangement in which the needle and bobbin assembly are not rotated, but a mechanism is provided for laterally shifting the workpiece relative to its direction of advance. U.S. Pat. No. 3,459,144 discloses a sewing machine wherein a workpiece is shiftable in X and Y directions to enable embroidery designs to be produced, an encoder supplies pulses to integrate X-Y table motion to work engagements of the stitching devices. These patents in the prior art, like all others in this category so far as known, do not rotate the needle and bobbin or other stitch-forming assembly about an axis, and hence lack the tangency or automatic angular control capability referred to above.